High optical transparent two-dimensional electronic conducting system and process for generating same

Abstract

Hybrid transparent conducting materials are disclosed with combine a polycrystalline film and conductive nanostructures, in which the polycrystalline film is “percolation doped” with the conductive nanostructures. The polycrystalline film preferably is a single atomic layer thickness of polycrystalline graphene, and conductive nanostructures preferably are silver nanowires.

Description

[0001]This invention was made with government support under DE-SC0001085 awarded by Department of Energy. The government has certain rights in the invention.BACKGROUND OF THE INVENTION[0002]A. Field of the Invention[0003]The present disclosure relates, generally, to transparent conducting materials (“TCMs”) and, more particularly, to hybrid TCMs including a polycrystalline film that is “percolation doped” with conductive nanostructures.[0004]B. Description of the Related Art[0005]Transparent conducting electrodes (TCEs) require high transparency and low sheet resistance for applications in photovoltaics, photodetectors, flat panel displays, touch screen devices and imagers. Indium tin oxide (ITO), or other transparent conductive oxides, have typically been used, and provide a baseline sheet resistance (RS) vs. transparency (T) relationship. However, ITO is relatively expensive (due to limited abundance of indium), brittle, unstable, inflexible. It increases in brittleness with aging...

AI Technical Summary

Benefits of technology

The invention is about a new type of transparent conducting material (TCM) that uses a combination of a granular polycrystalline film and conductive nanostructures (such as metallic nanowires) to create a highly efficient and flexible TCM. The conductive nanostructures are randomly dispersed throughout the polycrystalline film and are in contact with it. The density of the conductive nanostructures is below a percolation threshold, meaning they do not form a network for charge carriers. The TCM has high conductivity and transparency, with a sheet resistance below 20 ohms per square and a transmittance above 90% for solar radiation. The invention also includes a photovoltaic cell and a liquid crystal display that use the new TCM.

Problems solved by technology

However, ITO is relatively expensive (due to limited abundance of indium), brittle, unstable, inflexible.

It increases in brittleness with aging and is chemically unstable under acid / base conditions.

Furthermore, metallic-ion diffusion from ITO into thin barrier layers may result in parasitic leakage.

These and other problems make ITO-based technologies non-ideal for applications such as thin film photovoltaics (“PVs”), flexible electronics, touch-screen displays, light emitting diodes, and the like.

However, since resistivity and transmittance are often fundamentally constrained by the intrinsic properties of a material, developing TCMs with both low sheet resistance (e.g., RS90%) has been a persistent challenge.

Approaches involving welding of the nanowires, thermal annealing under pressure, or electroplating decrease RS by improving RNW-NW, but it has been challenging to reduce overall RS below ≈30Ω / □, especially for broadband T at 90%.

However, the exfoliated approach yields samples that are too small for practical applications, and large-area synthesis approaches, including chemical vapor deposition (CVD), typically involving growth on copper foil and subsequent transfer to an arbitrary substrate, produces grain sizes typically ranging from a few micrometers to a few tens of micrometers, depending on the specific growth conditions.

These high densities of CNTs or NWs, however, reduce the transmittance of such TCMs considerably.

Moreover, even with low RS, vertical current collection in PV cells is compromised by current crowding at the small-area interface between a network of CNTs or NWs and the bulk emitter layer.

Meanwhile, experimental data suggests that there is a fundamental limitation to the sheet resistance and transmittance of pure poly-graphene films, making it difficult for poly-graphene to compete successfully with ITO.

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